Erectile dysfunction is common, developing in 52% of men aged 40-70 years, and the host significant physiological correlate is increasing age. Independent of vascular disease, erectile tissue undergoes progressive loss of corporal trabacular smooth muscle and increase of corporal connective tissue. If clinicians were able to accurately measure in a non-invasive manner the degree of corporal fibrosis, they would be in a position to develop management strategies to prevent or delay the onset of erectile dysfunction. The clinical utility of an assessment of corpus cavernosum fibrosis is primarily early detection of initial structural disease, a critical component of erectile dysfunction prophylaxis. The broad, long-term objective of this engineering-based medical research is the development of a clinically-applicable method to assess corpus cavernosum fibrosis. The specific aims to achieve this goal will be to: (i) develop a refined engineering model that illustrates the relationship between cavernosal percent smooth muscle and cavernosal "expandibility". (2) demonstrate, in a group of patients, correlation between cavernosal "expandibility" (obtained during pre-operative dynamic infusion pharmacocavernosometry) and cavernosal percent smooth muscle (obtained by histomorphometric analysis of the cavernosal tissue harvested during penile implant surgery). This would verify that the correlation between these two parameters, which was shown to exist in a previous animal study, also exists in humans; and (3) clinically test a circular strain gauge device that automatically measures penile geometry versus intracavernosal pressure which is necessary for the calculation of cavernosal "expandibility". It is anticipated that this project will contribute substantially to a new clinical assessment of the structural effects of aging on erectile dysfunction which is necessary to develop rational effective clinical strategies to offset the age-related decline in erectile function.